1. Field of the Invention
The present invention relates to an automotive electronic control system that includes a commanding unit and a driving unit, both communicably connected to each other, and more particularly to such a system having a capability of detecting abnormality or malfunction in the commanding unit.
2. Description of Related Art
An example of a so-called Lan-Pulse system for detecting abnormality or malfunction in an electronic control unit is disclosed in JP-B2-58-55535. This system includes: a microcomputer for outputting signals for controlling loads, a watchdog circuit for detecting abnormality in the microcomputer and for outputting a reset signal; a fail-safe circuit for outputting a fail-safe signal in response to the reset signal; and a switching circuit for switching control signals of the microcomputer to a fail-safe side in response to the fail-safe signal. A signal synchronized with a machine cycle of the microcomputer, when a computer program is executed, is generated. It is determined that abnormality is involved in the microcomputer if the synchronized signal is not generated.
In the so-called Lan-Pulse system, however, there is a possibility that abnormality of the calculating function in the microcomputer may not be detected although an excursion of the microcomputer is usually found. If the computing malfunction or abnormality is not detected, actuators may be driven using the abnormally calculated value. To solve this problem, a method for detecting such abnormality with a plurality of microcomputers has been proposed. This method, however, makes the system expensive.
Further, if the Lan-Pulse system is used in a network in which plural electronic control units cooperate with one another, the Lan-Pulse has to be continuously outputted. Therefore, traffic in a communication bus is congested, and data may collide with one another and communication speed may be decreased. Accordingly, it is difficult to transmit the Lan-Pulse through the common bus, and a communication line exclusive for the Lan-Pulse has to be provided. This makes the system expensive.